The hope: that they can burn off at least some of the leaking crude before it reaches the gulf coast.
"No populated areas are expected to be affected by the controlled burn operations, and there are no anticipated impacts to marine mammals and sea turtles," said the Coast Guard in a statement. "In order to ensure safety, the Environmental Protection Agency will continuously monitor air quality and burning will be halted if safety standards cannot be maintained."
It is an inherently risky move, said engineers, but less risky than the alternatives.
"When you've got an oil leak like this, you use every tool in the toolbox to keep it offshore," said Edward Overton, a professor emeritus of environmental sciences at Louisiana State University in Baton Rouge. "If it gets to shore, it's going to coat everything with this sticky, gooey stuff and create a tremendous, awful mess."
The Deepwater Horizon drilling rig, operated by BP Oil and owned by Transocean Ltd., exploded and started burning April 20. Eleven rig workers were never found and are presumed to have died.
The Coast Guard said oil continues to spew from the wellhead, 5,000 feet beneath the surface of the gulf, at a rate of about 42,000 gallons per day. Satellite images show the resulting slick drifting north and eastward toward the coasts of Louisiana, Mississippi, Alabama and Florida.
"It's premature to say it's catastrophic," said Coast Guard Rear Admiral Mary Landry, who is leading the operation. "I will say it's very serious."
Some floating oil has come within 20 miles of shore. Adm. Thad W. Allen, commandant of the U.S. Coast Guard, told reporters in Miami today that depending on winds and weather, crews might have two to three days before oil hits land.
Gulf of Mexico Oil Spill: Crews Try Burning the Oil Slick
BP and its contractors are fighting a high-stakes battle to keep the spill from getting worse. They have tried, unsuccessfully so far, to cover the leaking wellhead with a dome or close it with a submersible robot. The company has said it is spending $6 million per day in the effort -- and the problem continues to grow.
Oil from the area is called sweet crude, but LSU's Overton said the name is deceptive. It contains heavy compounds, called asphaltenes, that do not burn easily or evaporate, even in the warm climate off Louisiana.
"When you've got a spill like this," said Overton, "there are three things you can do. You can burn it, scoop it up out of the water, or use chemical dispersants to break it up. This oil is not particularly good with any of those three."
"With light crude," he said, "you could burn most of it -- 70 or 80 percent. With heavy crude, I don't know. I'm not optimistic."
The disaster comes just weeks after President Obama announced he would open some parts of the continental shelf -- off limits since the administration of George H.W. Bush -- to oil exploration. Some proponents of drilling said Obama did not open enough areas; environmental groups, concerned about the marine environment and the burning of fossil fuels, used the Deepwater Horizon to say we-told-you-so.
"The volatility and fluidity of the oceans simply make it impossible for humans to safely produce and ship oil within that environment," wrote Carl Pope, chairman of the Sierra Club, in a blog post, "and because profit-driven companies will cut corners often enough to ensure that disaster results."
Overton said major oil spills are relatively rare -- which is why something like today's burn has not often been tried.
"You're talking big-league here," he said. "Keep your fingers crossed."
ABC News Radio and The Associated Press contributed to this report.